Carbon dioxide removal in indirect gasification - SGC

SGC Rapport 2013:277
Figure 8. Example of indirect gasification with the gasification bed to the left and
the combustion bed to the right, adapted from [19].
There are two alternative developments of indirect gasifiers, based on fluidized
bed technology, with commercial activities available in Europe at the time of writing
this report. This is the MILENA concept out of ECN [20] and the FICFB concept
out of TU Vienna [21]. The two systems for the synthesis of SNG was compared
in 2010 [4]. The FICFB-based concept is based on an integration of gasification,
gas filtering, and gas scrubbing and tar plays an important part. Since the
filter in the FICFB operates below 150°C, the tar dew point should be less than
150°C. Furthermore, the scrubber consumes RME to remove tars. FICFB aims at
relatively low tar production, contrary to the MILENA. The low tar yield in the
FICFB concept is achieved by using olivine as bed material and adding more
steam to the gasification; 5 times more steam is required in FICFB compared to
MILENA. The conversion of solid biomass in the gasification zone is relatively high
(90%) in FICFB and in the MILENA case 80-85% carbon conversion. Because of
the differences in conversion and steam consumption, the energy balances of
FICFB and MILENA are different. The FICFB gasification zone requires higher
heat influx to supply the energy for the endothermic reactions and steam heating.
The higher conversion also indicates a higher requirement for supplementary fuel
in the combustion art of the FICFB gasifier. The MILENA gasifier needs less energy
in the gasification zone, because conversion within the gasification zone is lower.
At the same time, more char is left to supply the heat for the gasification zone
from the combustion zone. But also the MILENA concept generally will require
supplementary fuel. In the MILENA process the tar from the gas cleaing system is
used as additional fuel. In the FICFB additional producer gas is recycled to supply
the additional heat.
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